[Someone1234]

I'd imagine people wanting to bypass this would still consume retail tobacco products via a 21+ proxy agent. I just think the cost of paying off a proxy would be cheaper than the cost of buying via some black market vendor (and low risk, since you're likely getting the real product via someone you likely know and trust).

Or just via common fake IDs that certain vendors will happily take, since it provides the vendor just enough legal protection for reasonable doubt.

Keep in mind that the new market for black market products is quite small (only people between 18-20), and the cost/risk of setting it up quite high. It could happen, but I think there are better alternatives to bypass this block-aid. It isn't really comparable to prohibition or the war on drugs, as those were/are global bans Vs. the entire population.